This project is concerned with an analysis of the activity of nerve cells in that system within the primate brain which is necessary and responsible for the process we refer to as attention. Monkeys trained to perform visually-guided go-no-go discrimination tasks are tested whilst extra cellular recordings are made from brain regions thought to be part of an attentional system. The most recent study in this series examined structures in the forebrain. We have learned that the dorsolateral perfrontal cortex as well as the area around the cingulate sulcus and the rostral neostriatum is well supplied with cells which respond to the manipulation of attention. This was accomplished by altering the reward value of the conditioned stimulus or by varying the waiting period preceding stimulus onset. These attention-related units have functional properties similar to those found in the brainstem reticular formation in previous studies by Bakay, Mirsky, Ray and colleagues. However, the attention cells appear to be more numerous in this region of the forebrain than in the brain stem. Moreover, the degree of plasticity we observed was apparently higher in the forebrain than in the brainstem reticular formation.